Sequential CT imaging tracing the progression of primary pulmonary mesenchymal chondrosarcoma arising from the wall of a pulmonary cyst: a case report

Background Mesenchymal chondrosarcoma (MC) is a rare, aggressive malignant tumour originating from chondroprogenitor cells and accounts for approximately 3–10% of all chondrosarcomas. MC typically arises within the axial skeleton or soft tissues; primary pulmonary MC is exceedingly rare. Case presentation We describe a rare case of primary pulmonary MC arising from a pulmonary cyst in a 58-year-old male with a 38 pack-year smoking history and bilateral bullectomy performed over 30 years previously. Computed tomography (CT) revealed progressive thickening of a cyst wall lesion in the right apical lung. Positron emission tomography with fluorodeoxyglucose (FDG-PET) revealed mildly increased uptake (SUVmax = 2.18); bronchoscopic cytology indicated class III atypical cells, which led to the initial suspicion of lung cancer. Video-assisted thoracoscopic right upper lobectomy with lymph node dissection was performed. Histopathology revealed a biphasic tumour comprising small round cells and cartilaginous differentiation, which was consistent with MC. This is the first reported case clearly demonstrating the progression of primary pulmonary MC on sequential CT scans. Conclusions We successfully documented the rare progression of primary pulmonary mesenchymal chondrosarcoma from an initially benign pulmonary cyst to a malignant tumour via sequential CT scans over a 14-month period. These finding from sequential imaging examinations highlight the crucial role of continuous radiological follow-up, enabling early recognition, accurate diagnosis, and timely surgical intervention for rare pulmonary malignancies.